The present invention is directed to optical devices and related methods. More specifically, the present invention provides a method and device for emitting electromagnetic radiation at high power using nonpolar or semipolar gallium containing substrates such as GaN, AlN, InN, InGaN, AlGaN, and AlInGaN, and others.
In the late 1800's, Thomas Edison invented the light bulb. The conventional light bulb, commonly called the “Edison bulb,” has been used for over one hundred years for a variety of applications including lighting and displays. The conventional light bulb uses a tungsten filament enclosed in a glass bulb sealed in a base, which is screwed into a socket. The socket is coupled to an AC power or DC power source. The conventional light bulb can be found commonly in houses, buildings, and outdoor lightings, and other areas requiring light or displays. Unfortunately, drawbacks exist with the conventional light bulb:                The conventional light bulb dissipates more than 90% of the energy used as thermal energy.        The conventional light bulb routinely fails due to thermal expansion and contraction of the filament element.        The conventional light bulb emits light over a broad spectrum, much of which is not perceived by the human eye.        The conventional light bulb emits in all directions, which is undesirable for applications requiring strong directionality or focus, e.g. projection displays, optical data storage, etc.        
In 1960, the laser was demonstrated by Theodore H. Maiman at Hughes Research Laboratories in Malibu. This laser utilized a solid-state flash lamp-pumped synthetic ruby crystal to produce red laser light at 694 nm. By 1964, blue and green laser output was demonstrated by William Bridges at Hughes Aircraft utilizing a gas laser design called an Argon ion laser. The Ar-ion laser utilized a noble gas as the active medium and produce laser light output in the UV, blue, and green wavelengths including 351 nm, 454.6 nm, 457.9 nm, 465.8 nm, 476.5 nm, 488.0 nm, 496.5 nm, 501.7 nm, 514.5 nm, and 528.7 nm. The Ar-ion laser had the benefit of producing highly directional and focusable light with a narrow spectral output, but the efficiency, size, weight, and cost of the lasers were undesirable.
As laser technology evolved, more efficient lamp pumped solid state laser designs were developed for the red and infrared wavelengths, but these technologies remained a challenge for blue and green and blue lasers. Lamp pumped solid-state lasers were developed in the infrared, and the output wavelength was converted to the visible using specialty crystals with nonlinear optical properties. Green lamp pumped solid-state lasers have 3 stages: electricity powers lamp, lamp excites gain crystal, which lases at 1064 nm, 1064 nm goes into frequency conversion crystal, which converts, to visible 532 nm. The resulting green and blue lasers were called “lamp pumped solid state lasers with second harmonic generation” (LPSS with SHG) and were more efficient than Ar-ion gas lasers, but were still too inefficient, large, expensive, and fragile for broad deployment outside of specialty scientific and medical applications. Additionally, the gain crystal used in the solid-state lasers typically had energy storage properties that made the lasers difficult to modulate at high speeds, which limited its broader deployment.
To improve the efficiency of these visible lasers, high power diode (or semiconductor) lasers were utilized. These “diode pumped solid state lasers with SHG” (DPSS with SHG) had 3 stages: electricity powers 808 nm diode laser, 808 nm excites gain crystal, which lases at 1064 nm, 1064 nm goes into frequency conversion crystal, which converts, to visible 532 nm. The DPSS laser technology extended the life and improved the efficiency of the LPSS lasers, and further commercialization ensued into more high-end specialty industrial, medical, and scientific applications. The change to diode pumping increased the system cost and required précised temperature controls, leaving the laser with substantial size and power consumption, while not addressing the energy storage properties which made the lasers difficult to modulate at high speeds.
As high power laser diodes evolved and new specialty SHG crystals were developed, it became possible to directly convert the output of the infrared diode laser to produce blue and green laser light output. These “directly doubled diode lasers” or SHG diode lasers had 2 stages: electricity powers 1064 nm semiconductor laser, 1064 nm goes into frequency conversion crystal which converts to visible 532 nm green light. These lasers designs are meant to improve the efficiency, cost and size compared to DPSS-SHG lasers, but the specialty diodes and crystals required make this challenging. Additionally, while the diode-SHG lasers have the benefit of being directly modulate-able, they suffer from severe sensitivity to temperature, which limits their application.
High power direct diode lasers have been in existence for the past few decades, beginning with laser diodes based on the GaAs material system, then moving to the AlGaAsP and InP material systems. More recently, high power lasers based on GaN operating in the short wavelength visible regime have become of great interest. More specifically, laser diodes operating in the violet, blue, and eventually green regimes are attracting attention due to their application in optical storage, display systems, and others. Currently, high power laser diodes operating in these wavelength regimes are based on polar c-plane GaN. The conventional polar GaN based laser diodes have a number of applications, but unfortunately, the device performance is often inadequate.